A court in eastern China has opened a rare trial of six corruption investigators accused of torturing to death a public sector engineer whom they were interrogating.

The defendants charged with causing intentional injury in the case include five members of the Communist Party's discipline inspection department and one local prosecutor. Their trial began Tuesday at a court in the city of Quzhou in Zhejiang province.

Prosecutors accuse the investigators of torturing 42-year-old engineer Yu Qiyi in April, by repeatedly dunking his head in a bucket of ice cold water during questioning until he drowned.

Relatives said Yu was detained in early March on suspicion of corruption in connection with a land deal. The engineer had been working for a state-owned company, Wenzhou Industry Investment.

Internal justice

As Yu also was a Communist Party member, authorities interrogated him under a secretive system called "shuanggui," a form of detention reserved for party officials suspected of disciplinary offenses.

Human Rights Watch Asia researcher Maya Wang said in an interview with VOA that detentions in shuanggui facilities happen outside of the law regulating China's criminal justice system.

"There are none of the procedural protections that usually exist in criminal procedures, so torture and mistreatment of individuals who are held in these facilities are quite common," Wang said. "The fact that we hear about it now is probably because of the government's anti-corruption drive, meaning that there are more officials ending up in these facilities."

Chinese President Xi Jinping ordered a tougher crackdown on official corruption after taking office earlier this year, warning that the problem threatens the ruling party's survival.

Under the crackdown, two other junior-level Chinese officials suspected of corruption have died in shuanggui detentions in recent months.

Suspicious deaths

In one case, a seismological official in central China's Hubei province, Qian Guoliang, died in June after suffering convulsions. Images on Chinese social media sites showed his body with bruises and sores.

In another case, a court official in central China's Henan province, Jia Jiuxiang, died in April after 11 days in custody. Authorities said the 49-year-old man died of a heart attack. Family members said his body also was bruised.

Beijing has done little to stop such abuses, Wang said.

"There are some efforts within the ordinary criminal procedure system to prevent torture, because news of torture, when it finds its way to the press, usually generates lots of outrage by Chinese citizens," she said. "So in recent years, the Chinese government has paid some more attention to this and instituted some reforms in the criminal procedure system. But these reforms have not meant better protection in the shuanggui system."

Lack of concern

Wang said many Chinese find it acceptable for corrupt officials to be detained under an internal party system that does not affect average citizens.

"Once somebody comes out of the system, they don't really want to talk about it because they are party members, unlike for example an ordinary person who was tortured in a police cell. So compared to the ordinary criminal procedure system, torture in the shuanggui system continues to persist and there is very little pressure from Chinese citizens to change that, and as a consequence there are not much procedural protections."

Chinese state-run media have said little about Yu's death.

A lawyer for Yu's family complained to Western news agencies that the court blocked him and a colleague from attending Tuesday's hearing. Lawyer Pu Zhiqiang also accused Chinese authorities of failing to prosecute more senior officials who may have ordered Yu's harsh interrogation.

Yu's ex-wife, Wu Qian, told Reuters, she believes there has been a cover up.